I. Field of the Invention
This invention relates to a flat bed for a fifth wheel tractor and, in particular, to a lightweight, demountable flat bed which quickly and easily converts a conventional fifth wheel diesel tractor to a flat bed truck.
II. Description of the Prior Art
Several attempts have been made to design a fifth wheel tractor which can be converted to a flat bed truck as required by the user. U.S. Pat. No. 3,117,804 to Bistrom discloses a tractor truck device with which includes an elevatable fifth wheel assembly which can be raised above the level of the truck bed. The fifth wheel assembly is attached to a lever arm which pivots upwardly when pushed by a V-shaped rocker arm. The rocker arm pivots about a point attached to the frame and is driven by an air cylinder. The rocker arm also cooperates with a ramp in such a way that, when the fifth wheel assembly is in a lowered position, the ramp is in a raised position to complete a flat bed. Conversely, when the fifth wheel assembly is elevated, the ramp is lowered to form a further guide for the kingpin. In either of the positions, the device includes pins which lock the components in their respective positions.
U.S. Pat. No. 4,475,740 to Strick discloses an articulated truck/trailer combination which includes a specially adapted fifth wheel tractor on which a flat bed or box housing can be placed, as well as a separate trailer designed to be towed in tandem behind the tractor/trailer combination. According to Strick, the tractor may also be used separately and has a fifth wheel assembly for cooperation with a conventional trailer. However, the tractor disclosed by Strick has several features with which significantly limit its utility. For example, a short cab tractor is required so that there is room between the back of the cab and the fifth wheel assembly to mount a flat bed or box like housing.
Moreover, the tractor is unconventional in that it has small diameter, i.e. fifteen inch, wheels so that the flat or box like housing rests at a conventional height of about 33 inches above the ground. Consequently, in order for the tractor to cooperate also with a standard trailer, it is necessary for the fifth wheel assembly to be elevated to its conventional height. For this purpose, Strick discloses a sliding lever arrangement which elevates the fifth wheel assembly to a conventional height.
Each of the previously known devices suffers from one or more of the following disadvantages; they are difficult to convert from use as a tractor/trailer combination to use as a truck; they require intricate mechanical linkages to raise and lower the fifth wheel assembly to a useful height; the linkages are heavy and expensive to manufacture and install, and are subject to periodic maintenance and/or failure; and the devices require specially adapted tractors and cannot be used with conventional fifth wheel tractors. These and other disadvantages are overcome by the present invention.